Various aromatic compounds are contained in woods and grasses, and various kinds of essential oil may be obtained from their leaves; blossoms, flowers, and their buds; barks, branches, stems and roots. Among these plants which contain such essential oil, there are crude drugs such as an aromatic stomachic, which have been used from ancient age. The essential oil, which is also the active ingredient for the crude drug, is a liquid mixture of several ten to two hundred compounds such as terpenoides, polyterpenoides, and phenols, and the rate of terpene is major.
As mentioned above, the essential oil may be obtained from various plants, but several essential oils obtained from trees such as Juniperus virginiana L., Cypress sempervirens L. var. stricta Ait., Chamaecyparis obtusa (Seib. et Zucc.) Endl. forma formosana Hayata, Juniperus utilis Koidz., Chamaecyparis obtusa Endl., Chamaecyparis formosensis Matsum., Thujopsis dolabrata Seib. et Zucc. var. Hondai Makino have anti-microbial activities or microbicide activities. Among such essential oils, it is known that hinokitiol contained in those obtained from Chamaecyparis obtusa (Seib. et Zucc.) Endl. forma formosana Hayata or Thujopsis dolabrata Seib. et Zucc. var. Hondai Makino has anti-microbial activities.
Hinokitiol is an acidic crystalline having a seven membered ring, and it is contained in the leaves or trees of Chamaecyparis obtusa (Seib. et Zucc.) Endl. forma formosana Hayata in Taiwan or the leaves, branches and stems of Thujopsis dolabrata Seib. et Zucc. var. Hondai Makino grown up in Aomori prefecture or Hokkaido.
Compounds detected as the components contained in the essential oils have a low molecular weight, and many of them are oily and a few of them are hydrophilic. Accordingly, it is difficult to mix the essential oil and water without using any surface active agent.
In general, oil and water can not be mixed homogeneously, but they may be mixed homogeneously depending on their mixing ratio. For example, a homogenous aqueous liquid can be prepared by extracting essential constituents with hot water from particular sources, soup for Chinese noodle or broth from a dried bonito is thus obtained. In such extract, a small amount of oil is dissolved in water. In the industrial process, for example, oil is vaporized by using contrabo to expose it to oxygen or other gas materials under pressure and at a certain temperature to allow the oil to mix with water.
However, the above-mentioned process includes the following problems. In the extracting process, the production cost is expensive, and it is impossible to produce such extract in a large scale. In the process by using contrabo, such extract may be produced in a large scale, but the cost is expensive. Furthermore, this process is performed under enhanced pressure and high temperature, the chemical structure of the objective components can be changed, and this makes it difficult to obtain an the aqueous extract containing the objective components.
Accordingly, such extracts can be used only for goods having high added value, for example, foods, food additives, and pharmaceuticals. Furthermore, in some cases, it is impossible to use aqueous extracts containing objective compounds with unchanged chemical structure.
It is known that hinokitiol is a compound having a seven-membered ring structure, and having excellent antimicrobial activity, particularly, antifungal activity, as well as it is safe compounds because resistant strains to hinokitiol scarcely appear. Therefore, wooden material from Chamaecyparis obtusa (Seib. et Zucc) Endl. forma formosana Hayata) has been used for a counter in sushi restaurant. Further, it is known that antimicrobial agents for washing having hinokitiol incorporated therein view of its antimicrobial properties.
On the other hand, hinokitiol has lower antimicrobial activities and no rapid action, as compared to antibiotics with high antibacterial activities and exhibiting rapid action. Accordingly, hinokitiol has been employed in the fields of dermatology, dentistry, and cosmetics.
Recently, however, an antibiotic resistant strain is increasing, particularly, methicillin-resistant multi-drug resistant Staphylococcus aureus, which is referred to as MRSA, appeared and causes troubles such as nosocomial infection. Recently, Kobori et al. have studied about antibacterial activity of hinokitiol to MRSA, and they reported that the appearing ratio of resistant strain to hinokitiol is low (Katsuji Kobori, et al., Medicinal Assay, vol.42, No.10, suppl. 1639(19)-1642(22)). Therefore, hinokitiol gathers attention.
However, as described above, since hinokitiol is one of the component contained in certain kinds of essential oil, which is insoluble in water, and impossible to mix homogeneously with water without any surface active agent, etc. On the other hand, when a surface active agent is used to mix them, the chemical structure of hinokitiol is changed and the antibacterial activity of hinokitiol is decreased. Therefore, since the antibacterial agent for washing could not be produced in liquid form, powdery one has been produced, but powdery one has poor handleable. Furthermore, the essential oils extracted from naturally occurring materials are highly safe for human bodies, in constant to those synthesized artificially, but their high production cost limits the application thereof.
Accordingly, there is a need to produce a homogenous aqueous solution that contains hinokitiol but does not contain any surface active agent with low cost.